The protective effect of rebamipide (CAS 11911-87-6), a novel anti-ulcer agent, was investigated in rats with hemorrhagic erosions on the glandular stomach induced by intragastric administration of 25 mg/kg of indometacin. Pretreatment with 100 mg/kg of rebamipide significantly inhibited the increase in total area of erosions in the stomach and the increase in lipid peroxides in the gastric mucosa. Rebamipide also inhibited the in vitro increase of lipid peroxides in the gastric mucosal homogenates induced by free radical initiators. These results indicate that rebamipide's protective effect against indometacin-induced gastric mucosal injury may result, in part, from its antioxidant effect, which inhibits lipid peroxidation.